The present invention relates to an electrophotographic photoreceptor (hereinafter occasionally referred to simply as a photoreceptor), and an electrophotographic image forming method, an electrophotographic image forming apparatus, and a processing cartridge.
In recent years, widely employed as organic photoreceptors (hereinafter referred simply to as photoreceptors), have been organic photoreceptors. Compared to other photoreceptors, organic photoreceptors exhibit advantages in that it is easy to develop materials which correspond to various types of exposure light sources ranging from visible light to infrared rays; it is possible to select materials which result in minimum environmental pollution; their production cost is lower, and the like. However, said organic photoreceptors exhibit disadvantages in that the mechanical strength is insufficient, and while producing numerous copies and prints, the photoreceptor surface tends to be degraded or abraded.
Since electrical and mechanical external force is directly applied to the surface of electrophotographic receptors upon employing charging units, developing units, transfer means, cleaning units, and the like, durability is required to counter such force.
Specifically required is durability to resist wear and abrasion of the photoreceptor surface due to friction, surface degradation due to active oxygen such as ozone, nitrogen oxides, and the like, which are generated during corona charging.
Heretofore, in order to improve the durability of organic photoreceptors, it has primarily been desired to minimize the wear due to sliding of cleaning blades and the like. In order to achieve said target, techniques have been investigated in which a very strong protective layer is applied onto the photoreceptor surface, and the like. For example, Japanese Patent Publication Open to Public Inspection Nos. 9-190004 and 10-251277 describe photoreceptors in which siloxane resins having a pronounced strength are employed in the surface layer. However, new problems are arisen because the highly strong protective layer comprised of the siloxane resins have low wear.
When the same organic photoreceptor is repeatedly used over an extended period of time, the residual potential increases due to its degradation caused by light, oxidation due to products formed by discharge, and the like. For example, an electric field generated by said residual potential results in electrostatic adhesive forces between paper dust which is charged with a polarity opposite to that of the photoreceptor. As a result, the adhesion of paper dust onto the photoreceptor surface is increased. Said adhered paper dust works as nuclei in such a manner that toner components and the like, such as fine toner particles and so on, are firmly adhered onto the photoreceptor surface, and photoreceptor filming is generated which may not be removed during a cleaning process. In the photoreceptor which exhibits a greater wear rate than the adhesion rate of paper dust and the like, it is possible to sufficiently remove electrostatically adhered materials. However, in photoreceptors which exhibit a lower wear rate as well as higher surface hardness, the adhesion rate exceeds the wear rate. As a result, said photoreceptor filming occurs.
In order to minimize said filming, heretofore, a decrease in physical adhesive force has been attempted by decreasing the surface energy of the protective layer. For example, Japanese Patent Publication Open to Public Inspection No. 10-83094 describes a method to use a protective layer having a small surface energy which results in a contact angle between the surface of the photoreceptor and water of at least 90 degrees. However, in the reversal development system in which during the transfer process, transfer media are charged in an opposite polarity to the photoreceptor, adhesive materials such as paper dust, and the like, generated from transfer media are charged in an opposite polarity to the photoreceptor and as a result, electrostatic adhesive force is generated between adhesive materials and the photoreceptor. Accordingly, it has been difficult to minimize the electrostatic adhesion of foreign materials, if the physical adhesive force of the photoreceptor surface is only decreased.
In order to overcome this drawback, investigation has been carried out. As a result, it has been discovered that by controlling an increase in the residual potential of the photoreceptor within the predetermined range, it is possible to minimize filming of developer materials as well as paper sheets. Further, it has been discovered that it is important to specifically control the rate of increase in the residual potential of the photoreceptor within a certain range with respect to the rate of the abrasive wear of the photoreceptor.
It is an object of the present invention to provide an electrophotographic photoreceptor which exhibits high durability and results in high image quality, and in more detail, to provide an electrophotographic photoreceptor which exhibits excellent stability of electric potential and minimizes filming, and to provide an electrophotographic image forming method, an electrophotographic image forming apparatus, and a processing cartridge employed in said apparatus.
The invention and its embodiments are described below.
1. An electrophotographic photoreceptor comprising a cylindrical electrically conductive support having thereon a plurality of layers, wherein layer thickness decreasing amount xcex94Hd (in xcexcm) is 0xe2x89xa6xcex94Hd less than 5xc3x9710xe2x88x926 per rotation, and residual potential variation amount is 0xe2x89xa6xcex94Vr less than 100 (in V) in the case an electric current corresponding to 0.1 C/cm2 is provided to a surface of said photoreceptor by charging and exposure.
One of a plurality of said resinous layers is preferably a surface layer, and said surface layer comprises a siloxane based resin containing structural units having charge transportability.
The surface layer preferably comprises colloidal silica.
The surface layer preferably comprises an antioxidant.
The cylindrical electrically conductive support preferably comprises a sublayer, a charge generating layer, a charge transport layer and the surface layer.
The charge generating layer comprises preferably titanyl phthalocyanine having a maximum peak at a Bragg angle of 27.2 degrees with respect to the Cu-Kxcex1 line.
The contact angle between the surface of the photoreceptor and purified water is preferably at least 90 degrees.
The electrophotographic image forming method comprising process of charging, image exposure, development, transfer and cleaning utilizing a blade, and employing an electrophotographic photoreceptor which comprises a cylindrical electrically conductive support having thereon a plurality of resinous layers, wherein when the image forming process is carried out by rotating said electrophotographic photoreceptor more than 300,000 times under conditions in which average toner amount adhered onto entire surface of said electrophotographic photoreceptor through development during said development process is at least 0.5 mg/cm2, a layer thickness decrease amount xcex94Hd (in xcexcm) per rotation is 0xe2x89xa6xcex94Hd less than 3xc3x9710xe2x88x926, and residual potential variation amount xcex94Vr (in V) per rotation is 0xe2x89xa6xcex94Vr less than 1xc3x9710xe2x88x925.
In the image forming method one of said plurality of layers is preferably a surface layer comprising siloxane based resin having structural units exhibiting charge transportability.
The cleaning blade, which is employed in said blade cleaning process, has preferably a hardness of 65 to 75 degrees and an impact resilience of 15 to 60 percent, and is brought into contact with said photoreceptor under a linear pressure of 5 to 50 g/cm.
The toner of a developer material employed in said development process is preferably blended with powder having a number average particle diameter of 10 to 300 nm as the external additive and external additive adhesion ratio Fd is between 10 and 90 percent, wherein
Fd=[1xe2x88x92{Sw1xe2x88x92Sw2}/Sw3]]xc3x97100
in the formula Sw1 is the BET specific surface area (in m2/g) of toner adhered to the external additive, Sw2 is the BET specific surface area (in m2/g) of toner prior to the addition of the external additive, and Sw3 is the BET specific surface area (in m2/g) of the external additive.
The toner of the developer material employed in said development process is preferably blended with powder having an average particle diameter of not more than 50 nm, and with powder having an average particle diameter of at least 60 nm in combination as the external additives.
The development process may employ the reversal development system.
In the image forming method the surface layer of the electrophotographic photoreceptor preferably comprises colloidal silica.
The surface layer preferably comprises an antioxidant.
The cylindrical electrically conductive support preferably comprises a sublayer, a charge generating layer, a charge transport layer and said surface layer.
In the electrophotographic photoreceptor the charge generating layer preferably comprises titanyl phthalocyanine having a maximum peak at a Bragg angle of 27.2 degrees with respect to the Cu-Kxcex1 line.
The contact angle between the surface of the photoreceptor and water is at least 90 degrees.
The electrophotographic photoreceptor is preferably repeatedly employed over at least 1,000,000 rotations for forming images.
An electrophotographic image forming apparatus comprising charging member, image exposure member, development member, transfer member and cleaning member utilizing a blade, and an organic electrophotographic photoreceptor which comprises a cylindrical electrically conductive support, having thereon a photosensitive layer, wherein when image forming process is carried out by rotating said electrophotographic photoreceptor more than 300,000 times under the conditions in which an average toner amount, adhered onto an entire surface of said electrophotographic photoreceptor comprising said surface layer, is at least 0.5 mg/cm2, through development of said development means, a layer thickness decrease amount xcex94Hd (in xcexcm) per rotation is 0xe2x89xa6xcex94Hd less than 3xc3x9710xe2x88x926, and residual potential variation amount xcex94Vr (in V) per rotation is 0xe2x89xa6xcex94Vr less than 1xc3x9710xe2x88x925.
In the electrophotographic image forming apparatus, one of said plurality of layers is preferably a surface layer comprising siloxane based resin having structural units exhibiting charge transportability.